Collaborative Research: Investigation of Deformation Mechanisms Governing the Tensile Ductility of Twinned Metal Nanowires

合作研究：控制孪晶金属纳米线拉伸延展性的变形机制的研究

• 批准号: 1410331
• 负责人: Ting Zhu
• 金额: $ 21万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1410331&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigation; Deformation; Mechanisms

Non-technical summaryRapid progress in nanotechnology is currently under way in that small structures and devices are being fabricated at the micrometer to nanometer scales. The reliable design of these structures and devices calls for an understanding of the mechanical properties of materials at small length scales. Metallic nanostructures like nanowires have been shown to exhibit ultra-high yield strength, on the order of one tenth of their elastic moduli. However, these metallic nanostructures usually have limited hardening, causing low tensile strain to failure. Such low ductility can severely affect the mechanical integrity of the constituent nanostructures in nanomechanical devices and other technological applications. There is currently a critical need to understand the fundamental deformation mechanisms governing the strain hardening and tensile ductility in metallic nanostructures. The proposed research synergistically integrates the in situ nanomechanical experiment and computational modeling to investigate the nearly unexplored strain hardening behaviors in metallic nanostructures. The results are expected to advance our fundamental understanding of deformation mechanisms governing the tensile ductility in metal nanowires and provide a mechanistic basis for the design of strong and ductile metallic nanostructures. Undergraduates will be recruited for summer research on this project. Collaborative research between the graduate students working on this project in Georgia Institute of Technology and North Carolina State University will promote their scientific exchange, increase team-work experience, and develop interdisciplinary expertise.Technical summaryThe metallic nanostructures such as nanowires usually exhibit ultra-high strength, but low tensile ductility, owing to their limited strain hardening capability. The objective of this proposal is to elucidate the deformation mechanisms governing the strain hardening and tensile ductility of an interesting type of metallic nanostructures - five-fold twinned Ag nanowires - which exhibit significant strain hardening in our preliminary experimental measurements. The proposed research involves three thrusts: (i) to perform the in situ nanomechanical testing to measure the tensile stress-strain responses and mechanical properties of individual nanowires; (ii) to perform the transmission electron microscopy characterization of pristine and deformed nanowires for investigation of the underlying dislocation mechanisms and particularly the effects of surface and twin boundary mediated defects; (iii) to conduct the molecular dynamics and transition state theory based atomistic modeling to elucidate dislocation mechanisms that control the strain rate and temperature effects on strain hardening and tensile ductility. The five-fold twinned nanowires studied in this project are different from the single-crystal nanowires, bulk nanocrystalline and nanotwinned metals in that the synergetic effects of free surfaces and coherent internal interfaces (i.e., twin boundaries with unique orientation parallel to the nanowire axis) can be critically important for controlling the dislocation mechanisms of hardening and related mechanical properties. The mechanistic insights gained from this project will be valuable to develop means to enhance the strength without a severe loss of ductility in a range of small-volume metallic materials.

非技术概述纳米技术的快速发展目前正在进行中，因为正在以微米至纳米尺度制造小结构和器件。这些结构和设备的可靠设计要求在小的长度尺度上理解材料的机械性能。金属纳米结构如纳米线已经显示出超高的屈服强度，大约是其弹性模量的十分之一。然而，这些金属纳米结构通常具有有限的硬化，导致低拉伸应变失效。这种低延展性会严重影响纳米机械装置和其他技术应用中的组成纳米结构的机械完整性。目前迫切需要了解金属纳米结构中应变硬化和拉伸延展性的基本变形机制。拟议的研究协同集成了原位纳米力学实验和计算建模，以研究几乎未开发的金属纳米结构的应变硬化行为。这些结果有望促进我们对金属纳米线拉伸延展性变形机制的基本理解，并为设计强韧性金属纳米结构提供力学基础。本科生将被招募为这个项目的夏季研究。格鲁吉亚理工学院和北卡罗来纳州州立大学的研究生之间的合作研究将促进他们的科学交流，增加团队工作经验，并发展跨学科的专业知识。技术摘要金属纳米结构，如纳米线通常表现出超高的强度，但低拉伸延展性，由于其有限的应变硬化能力。这个建议的目的是阐明一个有趣的类型的金属纳米结构的应变硬化和拉伸延展性的变形机制-五倍孪生银纳米线-表现出显着的应变硬化在我们的初步实验测量。本研究主要包括三个方面：（i）进行原位纳米力学测试，测量单个纳米线的拉伸应力-应变响应和力学性能;（ii）对原始和变形纳米线进行透射电子显微镜表征，以研究潜在的位错机制，特别是表面和孪晶界介导的缺陷的影响;（iii）进行以分子动力学和过渡态理论为基础的原子模拟，以阐明控制应变速率和温度对应变硬化和拉伸延展性的影响的位错机制。本项目研究的五重孪晶纳米线与单晶纳米线、块体纳米晶和纳米孪晶金属的不同之处在于自由表面和共格内界面的协同效应（即，具有平行于纳米线轴的唯一取向的孪晶界）对于控制硬化的位错机制和相关的机械性能是至关重要的。从这个项目中获得的机械见解将是有价值的开发手段，以提高强度，而不会严重损失的小体积金属材料的范围。